When a substrate-attached thin soft hydrogel film is immersed in water, swelling induces equibiaxial compression in the film. Upon a critical swelling ratio, the hydrogel surface becomes unstable and buckles into sharp self-contacts, referred to as "creases". This experiment may provide improved understanding on the buckling and folding processes in biological development. Imaged on a MFP-3D AFM using the BioHeater accessory. Scan size 90 µm. Image courtesy of Dayong Chen, University of Massachusetts-Amherst.